Summary of the ecological health of Auckland streams based on state of the environment monitoring 2000-2004

Author:

John Maxted

Source:

Auckland Regional Council

Publication date:

2005

There are approximately 10,000 km of streams in the Auckland region (mainland) as mapped on 1:50,000 scale NZMS260 series topographic maps (ARC 2001). This is an underestimate of resource extent because many small streams are not mapped, and the mapping does not include ephemeral and intermittent streams that flow only during certain times of the year or during rainfall events. Research is underway to assess the extent, quality, functions of intermittent and ephemeral streams, and will be reported in future annual reports. In the narrow Auckland isthmus, catchments and their streams are small with 90% first and second order with a channel width of less than 2 metres. The data used to derive the following assessment summary were taken largely from these small wadeable mapped streams.

The vast majority of Auckland streams are in rural land uses, presenting 63% of the region by area (Figure 1). The remainder of the region is in native forest, urban, and commercial forestry land uses (Figure 1). These estimates were derived from 2002 satellite imagery (Ministry for the Environment, MfE, 2004). Further, the majority (approximately 95%) of Auckland streams affected by human activities are in “softrock” geology including clay and sand. The area of the region in “hard-rock” geology (e.g., cobbles and boulders) is limited to the Waitakere and Hunua ranges and mostly in protected native forest catchments.

The physical, chemical, and biological conditions of Auckland “soft-bottomed” (SB) streams is summarized below, utilizing data collected from a network of 41 sites representing the four major land use classes and two level of disturbance. Sites in each land use class (except the native forest reference class) were selected with “low” and “high” levels of human activity and disturbance. This site network provided the basis for delivering assessment results to a wide range of non-scientific decision makers including managers, planners, politicians, and the general public. These results are taken from a report documenting the development of a new biotic index for SB streams (Stark and Maxted 2004)...